Electrical Test Equipment

Electrical Test Equipment Examples

AC/DC True RMS Clamp Meter

• example: Fluke 337 1000 Amp True RMS AC/DC Clamp Meter

The True RMS Meter Explained

New solid state components often conduct non-sinusoidal (distorted) or non-linear loads. In other words, the current occurs in short pulses rather than the smooth sine wave drawn by a standard induction motor. The current wave shape can have a drastic effect on an amperage reading.

There are two types of current clamps commonly available: “Average Responding” and “True RMS”. The average responding meters are widely used and are lower cost. They give a correct reading for linear loads such as standard induction motors, resistance heating, and incandescent lights. But when loads are non-linear, containing semiconductors, the “average responding meters” typically read low. If the load contains power semiconductors, rectifiers, SCRs, etc. a cheap meter will not give an accurate reading.

In an AC circuit, voltage and current are continually varying, from zero up to their maximums, then back to zero again. Therefore, the effective voltage and current will be less than their maximum values. Values such as 120 volts and 10 amps are the Effective Values (also called Root-Mean-Square, or RMS values), which are equal to .707 times the maximum values.

Currents containing harmonics can only be measured accurately with a “True RMS” (TRMS) instrument. A TRMS instrument will read accurately under all load conditions. An average responding multimeter or clamp-on meter will read a sine wave accurately as long as we have linear loads without harmonics.

Determine Current Draw of AC Electrical Circuit

A circuit breaker is an electrical device used in an electrical panel that monitors and controls the amount of amperes (amps) being sent through the electrical wiring. Circuit breakers come in a variety of sizes. For instance, 10, 15 and 20 amp breakers are used for most power and lighting needs in the typical home. Some appliances and specialty items (washers, dryers, freezers, whirlpools, etc.) will require a larger circuit breaker to handle the electrical load required to run that appliance.

It is important to know the amperage of a circuit breaker so you don't overload the breaker with too many appliances. An overloaded circuit can cause a fire in wiring or generate excessive heat in the circuit box.

1. Find the data plate on the device you are trying to wire.
2. Find the section labeled FLA or LRA, this is the full load. In many instances, the load will be expressed in watts, IE 3800 watts FL.
3. Divide the wattage by the voltage of the circuit, in the USA usually 120 0r 240.
4. The result is the amperage the device draws.
5. Multiply by 1.25, the National Electrical code requires protection at %125.
6. Install circuit breaker to meet that size. Standard branch circuits like lighting require 15 amp. Appliance circuits, IE kitchen, require 20 amp.

• Never replace a 15A or 20A fuse in a fuse box with a 30A fuse
• 30A fuses and breakers are rarely used in a residential circuit box

For dependability and long life of electrical equipment most electricians like to see a circuit loaded to only .8 of it’s rated capacity. If you had a 20-amp circuit and multiply it by .8 you would get 16 or the highest amp draw the electrician would like the circuit to handle. Industrial multipliers are lower, somewhere between .70 and .75.

Electrical Test Equipment Suppliers

• Hoyt Electrical Equipment - http://www.hoytmeter.com/
• Test Equipment Depot - http://www.testequipmentdepot.com/
• Advanced Test Equipment Corporation - http://www.atecorp.com/